Ophthalmic lenses such as contact lenses, and in particular soft contact lenses for single use, are produced in an automatic lens manufacturing process with the aid of automatic manufacturing lines. In such an automatic manufacturing line, the contact lenses are typically formed using molds comprising male and female molds. In the following, the terms “mold” or “molds” are used to include or denote a “mold half” or “mold halves”, respectively, unless the specification explicitly suggests otherwise. A flowable lens forming material is dispensed into one of the molds, for example into the female mold, and the male and female molds are then mated to enclose the lens forming material between the molding surfaces of the male and female mold to define the shape of the contact lens. Thereafter, the lens forming material enclosed between the molding surfaces is cured to form the contact lens, the mold is opened and the contact lens is removed from the male or female mold for further processing.
The individual manufacturing steps of the automatic lens manufacturing process are carried out at various different process stations in such automatic manufacturing line, and the process steps are concurrently carried out in such process stations for a plurality of lenses. For example, lens forming material is dispensed into a plurality of molds at the same time, the plurality of molds is then transported together to a process station where the male and female molds are concurrently mated, the plurality of mated molds are then transported together to the curing station where the lens forming material is cured, and so on.
During mating the male and female molds, the male and female molds must be properly aligned relative to each other in order to make sure that the contact lens defined by the molding surfaces of the mated male and female molds has the desired geometry. To provide for proper alignment of the male and female molds, in a known process and manufacturing line the male and female molds are provided in rigid mold carriers each carrying two molds of the same type, for example two male molds or two female molds. The male molds and the female molds are fixedly mounted in sleeves which are rigidly mounted to the respective mold carrier. The sleeves axially extend beyond the molding surfaces of the respective molds. During the process of mating the male and female molds the sleeves of the male and female molds come into telescopic engagement with each other, and once they are in telescopic engagement the mold carriers are further moved towards each other to a final position in which an abutment portion of the sleeve of the male mold abuts against a corresponding abutment portion of the sleeve of the female mold. In this final position the male and female molds of that mold are in proper alignment and have the proper position relative to each other so that the contact lens formed by that mold has the desired geometry.
Obviously, this requires that the sleeves of the mold carrier carrying the two female molds and the sleeves of the mold carrier carrying the two male molds must be very precisely mounted to the respective mold carriers, since due to their rigid mounting to the respective mold carrier only a small deviation of a sleeve from its set position is possible, otherwise the associated sleeves of the mold carrier carrying the male molds and of the mold carrier carrying the female molds cannot get telescopically engaged. Since only very small deviations from the set position are tolerable, mold carriers carrying only two molds are used.
On the other hand, as has been outlined above a plurality of molds of the same type, for example ten to fourteen molds, are typically concurrently processed in one processing station in order to make the manufacturing process highly effective. Accordingly, five to seven such carriers each carrying two molds of the same type are transported in a “pack” to the mating station. This transport is achieved with the aid of conveyor belts on which the pack of mold carriers is placed. As the pack of mold carriers arrives at the processing station, the foremost carrier of the pack of mold carriers hits a positioning stopper making the entire pack of mold carriers abruptly stop. This abrupt stopping of the mold carriers of the pack leads to wear of the conveyor belts slipping underneath the carriers.
At the mating station it must be confirmed that each of the carriers of the pack has safely arrived. This is achieved with the aid of optical sensors (light barriers). However, such light barriers are prone to errors. By way of example, a small water droplet may partially or entirely cover the receiver of the light barrier so that the receiver may produce a signal representative of a carrier being present although actually there is no carrier present.
In the mating station, the sleeves of each carrier carrying the two female molds must be individually aligned with the sleeves of the associated carrier carrying the two male molds. This alignment is performed with the aid of so-called “positioning rakes” having positioning prongs which force the individual sleeves (and the carriers) into the desired set position. This positioning is performed both for the carriers carrying the female molds and for the carriers carrying the male molds. Thereafter, the sleeves of all carriers carrying male molds can reliably get into telescopic engagement with the sleeves of the corresponding carriers carrying female molds. However, due to some of the individual sleeves (and consequently the carriers) of the pack having to be significantly displaced (the displacement can amount up to some millimeters) from their original position after arrival in the mating station to the set position in which they can reliably get into telescopic engagement with their associated sleeves, this positioning step may lead to high mechanical wear of the positioning prongs.